12 volt Battery Questions

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by Alan Sailer, Sep 7, 2021.

  1. Alan Sailer

    Alan Sailer New Member

    Joined:
    Sep 7, 2021
    7
    1
    0
    Location:
    California
    Vehicle:
    2007 Prius
    Model:
    One
    Two days ago my 2007 Prius started a series of cascading failure starting with the air conditioner, escalating to a bunch of warning lights and ending with engine shutdown.I did get home.

    After a few minutes searching a bad 12 mvolt battery seemed the most likely cause. The displayed diagnostic showed a battery voltage of 11.4.

    I pulled the battery, it read 11.7 so I tried charging it overnight to 14.4 volts. A battery tester (load type) showed that the battery was on the low side of good. So I decided to buy a new battery. After installing it the car works fine.

    My question is basically how I can tell if the charging system is treating the new battery well? The battery indicated 11.9 volts next morning, after starting the car is was a steady 14.1 volts as I drove away. At work the battery was 12.8 volts.

    My old experiences with classic flooded lead-acid batteries is that anything below 12 volts is a dead battery. So a new AGM battery reading 11.9 worries me.

    Another worrisome observation is that with both the old battery and the new battery, flashing the headlights (while trying to get into the diagnostics mode) causes the clock display to radically dim. Which suggests the battery voltage is dropping.

    Any pointers will be appreciated.

    Cheers.
     
  2. SFO

    SFO Senior Member

    Joined:
    Feb 7, 2017
    4,117
    3,846
    0
    Location:
    Northern California
    Vehicle:
    2007 Prius
    Model:
    N/A
    Welcome to PriusChat!!

    How many miles on the vehicle, and when was the last time the inverter coolant pump was replaced?
    Unlikely that your 'failure' was related to the 12v source. My WAG is it was a failing inverter coolant pump (DTC P0A93).

    Instead of guessing, find a hybrid compatible OBD2 code scanner and post any retrieved codes (DTCs) in this thread for further guidance.
     
  3. Alan Sailer

    Alan Sailer New Member

    Joined:
    Sep 7, 2021
    7
    1
    0
    Location:
    California
    Vehicle:
    2007 Prius
    Model:
    One
    SFO,

    Wow! Never would have gone there. A data point was that this happened on a hot day, 86F..

    Car has basically 200K and no replacement of the inverter cooling pump. Which I didn't even know exited.

    I'd do some searching and educate myself. A friend has an OB2 scanner so off I'll go to beg to use it.

    Cheers
     
    SFO likes this.
  4. sam spade 2

    sam spade 2 Senior Member

    Joined:
    Mar 31, 2018
    5,600
    2,232
    0
    Location:
    USA
    Vehicle:
    2017 Prius c
    Model:
    Four
    As it should.
    Your "new" battery might not have been anywhere close to fully charged to begin with.
    Recent vintage AGMs should be around 12.9 when new and full.

    And the onboard system charging system charges very slowly.
    So if your daily trips are short, it may STAY low for a long time which is not good.

    NOW you should charge the new battery at 14.4 overnight and then see what happens from there.

    SFO might be right. Or you might have a loose main 12 V cable connection.
    Or you might have developed a parasitic drain from something.
     
  5. Alan Sailer

    Alan Sailer New Member

    Joined:
    Sep 7, 2021
    7
    1
    0
    Location:
    California
    Vehicle:
    2007 Prius
    Model:
    One
    Interesting. Pump is under the right headlamp. And it looks like a working pump will cause agitation of coolant
    in the reservoir.

    I am lost about changing the fan speed. Looks like some sort of re-programming of the on-board electronics.

    Thanks again.

    Sam spade,

    Good information. I can charge up the battery and see what happens. And the main 12 volt cable is the 12 volt battery connection? Or something else?

    Cheers.
     
    #5 Alan Sailer, Sep 7, 2021
    Last edited: Sep 7, 2021
  6. Alan Sailer

    Alan Sailer New Member

    Joined:
    Sep 7, 2021
    7
    1
    0
    Location:
    California
    Vehicle:
    2007 Prius
    Model:
    One
    So I got home and ran a simple test to check the inverter cooling pump. Two presses of the power button (no brake) to get into IG_ON.
    I removed the coolant filler cap and looked inside. I saw no circulation of coolant. I also heard (or felt) no pump vibration.

    Is this a good test for the pump?

    Cheers.
     
  7. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    94,221
    42,709
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    changing fan speed is part of sfo's signiture, not directed at you.

    the new 12v should read close to 13 volts after sitting overnight, if it has been fully charged,

    'main 12v cable' is the positive cable on the battery. but make sure both are clean and snug, and also negative to ground,
    if the 12v is low in the morning after a full charge, there might be a drain in the system. to e figure out if it is a drain or bad battery, simply charge it again, and disconnect the negative cable.
    if it is still low in the morning, the battery is bad. if not, something in the car is draining it.
     
  8. Alan Sailer

    Alan Sailer New Member

    Joined:
    Sep 7, 2021
    7
    1
    0
    Location:
    California
    Vehicle:
    2007 Prius
    Model:
    One
    bisco,

    Thanks. I'm pretty sure the new battery is charged and good. The reading was 12.6 today after my 20 minute commute. I will check it tomorrow to see if it had fallen much.

    And also thanks for the ID on sfo's signature. I am happy that I don't have to learn anything about HV battery fans :)

    Cheers.
     
  9. SFO

    SFO Senior Member

    Joined:
    Feb 7, 2017
    4,117
    3,846
    0
    Location:
    Northern California
    Vehicle:
    2007 Prius
    Model:
    N/A
    Yes, if the vehicle is 'on' or 'ready', and you can't "feel" the pump working then it has likely failed without blowing the AM2 fuse.

    If you've never had the inverter coolant pump replaced before, you may be eligible for campaign "C0U" at the local dealership.

    Many OEM pumps will last around 100k miles, and the aftermarket options could fail sooner. Nice to know this one made it 200k.
     
  10. Alan Sailer

    Alan Sailer New Member

    Joined:
    Sep 7, 2021
    7
    1
    0
    Location:
    California
    Vehicle:
    2007 Prius
    Model:
    One
    sfo,

    I think I'm done here. I'll get the pump and put it in. The new battery is 12.5 in the morning o it's good.
    The old battery probably had a while left to go but not a big deal.

    Thanks for all the help everyone.

    Cheers.
     
  11. sam spade 2

    sam spade 2 Senior Member

    Joined:
    Mar 31, 2018
    5,600
    2,232
    0
    Location:
    USA
    Vehicle:
    2017 Prius c
    Model:
    Four
    Yes. But there also is a main NEGATIVE cable which attaches to the body or frame somewhere.
     
  12. Alan Sailer

    Alan Sailer New Member

    Joined:
    Sep 7, 2021
    7
    1
    0
    Location:
    California
    Vehicle:
    2007 Prius
    Model:
    One
    sam spade 2,

    Thanks. Both cables were removed from the old battery and attached to the new. The battery looks electrically perfect with 12.5v in the morning and 14.4 volts driving.

    My efforts are now towards replacing the dead inverter coolant pump.

    Cheers.
     
  13. sam spade 2

    sam spade 2 Senior Member

    Joined:
    Mar 31, 2018
    5,600
    2,232
    0
    Location:
    USA
    Vehicle:
    2017 Prius c
    Model:
    Four
    But.....were the cables COMPLETELY removed, that is, the connections at both ends were taken off and put back on ??
    For a total of 4 connection points ??

    12.5 in the morning is not "perfect". A brand new, fully charged battery should be around 12.8.

    Whatever you measure while driving is NOT the battery itself but is the voltage coming from the charging system.
    14.4 is OK but might be a bit high, indicating that the battery still is not fully charged and the system is trying to get it up higher.
     
Loading...